LUNAR EXPLORATION CONCLUDED

To the Lunar Highlands: Descartes

Two landing sites had been seriously considered for Apollo 16, the
crater Alphonsus, 300 miles (480 kilometers) south of the moon's center,
and the region some 340 miles (550 kilometers) east-southeast of the
moon's center, north of the ancient crater Descartes. In both places
geologists thought they would find highland material differing in
composition from the Fra Mauro samples and the basalts filling the
maria. The wall of Alphonsus was, some argued, pre-Imbrian highlands
material, while dark craters on its floor were thought to consist of
relatively young volcanic material that might have originated at great
depths. North of Descartes, two formations (Cayley and Descartes) were
of major interest. Evidence indicated that both were volcanic but of
different types and ages. The area is the highest topographic region in
the highlands on the visible face of the moon, indicating that the
Descartes volcanics represent remobilized highlands. Analysis of these
materials was expected to clarify the basic processes that formed the
highlands.59

Preliminary discussions among interested scientists considered both
sites but did not entirely agree on either.60 Alphonsus remained a strong candidate, but in
view of the fact that it would be preferable to have more results from
Apollo 14 and 15 before landing there, Descartes was preferred for
Apollo 16. With one more mission left, Alphonsus could still be visited.
The Apollo Site Selection Board approved Descartes as the landing site
for Apollo 16 at its meeting on June 3, 1971.61

Science plans for the Descartes mission were much the same as they had
been for Hadley Rille: to inspect, survey, and sample materials and
surface features in the landing area; emplace and activate the lunar
surface experiments; and conduct photography and remote sensing of the
moon from lunar orbit. The surface package included two new instruments:
a magnetometer and, in place of Apollo 15's suprathermal ion detector,
an active seismometer that would be excited by several explosive charges
after the astronauts left. Another new experiment was an automatic
far-ultraviolet camera and spectrograph to photograph several galaxies
from the moon's surface. Its objective was to study the distribution of
interplanetary and intergalactic hydrogen.62

Apollo 16 blasted off from Kennedy Space Center at 12:54 p.m. Eastern
Standard Time on April 16, 1972. Command module Casper and
lunar module Orion arrived in lunar orbit three days later.
All systems functioned well until Orion separated from the
command module; a malfunctioning component in the main propulsion system
caused Houston to delay the lunar module's descent for nearly six hours
while it was checked out. When Mission Control was satisfied,
Orion fired its descent engine and landed easily on the
plain at Descartes at 9:33 p.m. EST on April 20.63

In the next 71 hours mission commander John Young and lunar module pilot
Charles Duke laid out the surface instruments and conducted three
traverses in their lunar rover, covering in all some 27 kilometers
(nearly 17 miles). While they were busy on the surface, Ken Mattingly in
Casper was occupied with operating the instruments in the
service module. The only serious mishap on the surface occurred when
Young tripped over the cable to the heat-flow sensors, pulling it loose
from the central station and incapacitating the experiment.64

Young and Duke finished their exploration, loaded the 96 kilograms (210
pounds) of samples they had collected into Orion, and
rejoined Mattingly in lunar orbit on April 23. They released the
moon-orbiting subsatellite, but because of recurring problems with the
service propulsion system, the spacecraft was not in the optimum orbit
for the satellite. As a result, the satellite crashed into the moon
after only five weeks.65 During the
four-day return flight they conducted additional experiments with
electrophoresis, a technique that offered advantages for separating
certain biological preparations that could not be efficiently done in a
gravity field. A normal landing in the Pacific, north of Christmas
Island, completed the mission On April 27.66

Even before the Apollo 16 rock samples had been returned to Houston it
was apparent that premission interpretations of the Descartes site had
not been accurate. The service module instruments showed abnormally low
radioactivity and high aluminum-silicon ratios in the area - both
characteristic of typical lunar highlands. Furthermore, the laser
altimeter found that the extensive plateau on which the site lay was
almost four miles higher than the surrounding terrain, an elevation that
seemed impossible to achieve by buildup of volcanic material.67 Preliminary examination of the samples
confirmed what scientists had suspected as soon as Young and Duke began
to explore: the site was not volcanic. Most of them appeared to be
impact breccias rather than basalts.68
This result, confirmed by later analyses, "forced a reevaluation of
the process of photogeology and site selection," because the
majority opinion before the mission had affirmed that the site was
volcanic in origin.69

The more samples returned from the moon the less clear the picture of
its origin and evolution became to scientists. At the third lunar
science conference, which included presentations of information from
Apollo 15 and the Soviets' Luna 16, a more comprehensive picture of the
moon was evident, but fewer investigators would claim to understand its
evolution. The best summary at the time seemed to be that the moon is
now relatively cold and inactive but that it has gone through a complex
sequence of melting and resolidifying by internal or external heating.70 Toward the end of 1972 one baffled
scientist, Gerald Wasserburg, summarized the frustrations of the lunar
scientists: "we've got answers but not the questions," he
said. "I'm not sure we're asking the questions in exactly the right
way."71

64. Baldwin, "Mission
Description." The cable incident was the first to knock out an
experiment, but every mission had experienced similar problems with
cables that would not lie flat on the lunar surface. Furthermore, the
space suits did not permit astronauts to see their own feet.
Nonetheless, it caused one columnist to splutter, " . . . what we
have been watching [is not] science. Those two klutzes up there on the
moon, bumping into each other, unable to repair what their clumsiness
has damaged, didn't look like scientists or lab technicians even. They
looked like . . . a couple of miscast wahoo military officers. Nicholas
von Hoffman, Two Klutzes On the Moon," Washington
Post, Apr. 24, 1972. Von Hoffman was rather hyperbolically
protesting the continuation of Apollo and the amount of time devoted to
coverage of the missions by the television networks.